Stealing Deals With the Devil as ???

The method is pretty easy - you need a way to become invincible - The Polaroid or an invincibility item and 3 soul hearts (Blue Baby starts with 3 souls hearts).

How the process is done:
Part 1: Activate your invincibility item / The Polaroid (just hurt your self using the fire ).
Part 2: Walk into the item you want.
Part 3: You got the item.

Yeah... It's that simple.
By the way: you can use this method with every charchter in the game, but it will work only with souls hearts Deals With the Devil.

Book of Shadows - 3 Rooms recharge:
Grants Isaac invulnerability for 10 seconds.

My Little Unicorn - 6 Rooms recharge:
Grants Isaac invincibility for a short period of time. Isaac cannot fire tears during the invincibility effect, but he can damage enemies by touch.

A Pony - 4 Rooms recharge:
Upon use, Isaac will charge in the direction selected, and will become invincible during the charge, allowing him to damage enemies by touch. While equipped, passively increases Speed by 2, and grants Isaac Flight.

White Pony - 6 Rooms recharge:
Upon use, Isaac will charge in the direction selected and deal damage to monsters. In addition, beams of light (Similar to Crack The Sky) drop down in random locations around the room, damaging any enemies that touch them. While equipped, passively increases Speed by 2, and grants Isaac Flight.

Celtic Cross - Passive item:
Has a 20% to create a protective shield around Isaac upon taking damage, which grants him invulnerability to all forms of damage for 7 seconds.